1. Field of the Invention
The present invention relates to a method for manufacturing polycrystalline silicon, which is for manufacturing a polycrystalline silicon rod by depositing polycrystalline silicon on a surface of a heated silicon seed rod.
Priority is claimed on Japanese Patent Application No. 2007-307445, filed Nov. 28, 2007, the content of which is incorporated herein by reference.
2. Description of the Related Art
As one of methods for manufacturing polycrystalline silicon, there has been known a so-called Siemens method used for manufacturing polycrystalline silicon. This method includes heating a plurality of silicon seed rods, arranged within a reaction furnace, supplying a raw material gas which is a mixed gas of chlorosilane gas and hydrogen gas into the reaction furnace thereby bringing the raw material gas into contact with the heated silicon seed rods, and allowing polycrystalline silicon to deposit on surfaces of the silicon seed rods by pyrolysis and hydrogen reduction of the raw material gas.
For such a method for manufacturing polycrystalline silicon, silicon seed rods which serve as seed cores are fixedly stood on respective electrodes arranged on an inner bottom part of the reaction furnace, with the upper portion of each of the silicon seed rods connected to each other by device of a short connecting member to thereby form a Π shape. A plurality of raw material gas ejection nozzles is dispersively-arranged between the erected silicon seed rods in the inner bottom part of the reaction furnace. When an electric current is applied from the electrodes to the silicon seed rods, the silicon seed rods are heated due to the resistance. Thus, when the raw material gas ejected from the ejection nozzles comes into contact with the surfaces of the silicon seed rods, polycrystalline silicon is deposited and grown in a radical direction to form silicon rods.
In this connection in the prior art, as disclosed, for example, in Japanese Patent No. 3660617, a control is needed to keep the rod surface temperature and the supply amount of the raw material per unit area of the rod surface in respective predetermined ranges until the termination of a deposition except for an initial stage of the deposition. In other words, since the surface area of a silicon rod increases with the growth of the silicon rod, the amount of raw material gas to be supplied is increased in accordance with the growth of the silicon rod.
However, when there is a large number of silicon seed rods thereby becoming closely packed together, there occurs a problem that it may become difficult to uniformly supply the raw material gas to the surface of the silicon seed rods, which results in undesired shape, such as giving an rough surface to silicon rods, and thus lowers the proportion of polycrystalline silicon with a smooth surface which is necessary to be suited as a raw material for manufacturing single crystal silicon. As disclosed in Japanese Patent No. 3660617, the method of merely increasing the amount of raw material gas to be supplied with growth of silicon rods requires an enhanced supply facility and thus grows in cost.
In consideration of the above circumstances, an object of the present invention is to provide a method for manufacturing polycrystalline silicon, which allows producing a larger amount of high quality polycrystalline silicon having smooth surface morphology by effectively preventing a silicon rod surface from being malformed.